This application claims priority to an application entitled xe2x80x9cMETHOD OF MANUFACTURING TAPERED OPTICAL WAVEGUIDE,xe2x80x9d filed in the Korean Intellectual Property Office on Jul. 3, 2002 and assigned Serial No. 2002-38169, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a method of manufacturing an optical waveguide, and more particularly to a method of manufacturing a tapered optical waveguide, through which two optical waveguides of different sizes are connected optically.
2. Description of the Related Art
A waveguide is an indispensable element of an integrated optical component in a high-speed optical-communication network. The waveguide has wide applications used in optical-power splitters, optical couplers, optical modulators, interferometer-based switches, semiconductor lasers, and planar devices for dense wavelength-division-multiplexing communication.
FIG. 1 is a schematic diagram of a wavelength-division multiplexer utilizing an arrayed waveguide grating. The waveguide grating includes input and output waveguides 11a and 11b, two planar waveguides 13a and 13b, and an arrayed waveguide grating 15. In the multiplexer shown in FIG. 1, portions encircled by broken linesxe2x80x94that is, portions in which the width of a waveguide or waveguides abruptly changesxe2x80x94necessarily require some modification of the waveguide or waveguides. When optical waveguides with different constructions are connected with each other directly, the difference in the width of adjoining optical waveguides generates optical loss. This n abrupt change between the connecting joints causes an optical signal to be radiated instead of being propagated through the waveguides. This radiation of the optical signal generates additional loss and noise, thereby causing cross-talk between different channels.
In order to overcome the problems described above, a tapered waveguide, which is inserted between two different widths to connect with each other optically, has been employed.
FIG. 2 is a schematic view of a conventional linear tapered waveguide. As shown, the tapered waveguide 22 has a width increasing from one end of a base waveguide 21 to the other end of a target waveguide 23. However, a lateral taper and a vertical taper must be simultaneously realized in order to lower the coupling loss caused by a mode mismatch. In the conventional method of realizing the vertical taper, a thin film having a thickness profile is deposited and then etched by means of a shadow mask, thereby forming a tapered waveguide. In another method, a thin film having a uniform thickness is etched by a shadow mask, while an etched depth of the thin film is adjusted to allow the thin film to have a thickness profile, then the thin film with the thickness profile is etched again, thereby forming a tapered waveguide. However, in the conventional methods utilizing a shadow mask, it is difficult to control a position, inclination, shape, etc., of a tapered section and to mass-produce tapered waverguides as the shadow mask must be installed above a substrate.
According to another conventional method of manufacturing a tapered waveguide, a thin film is deposited on a stepped substrate, then a flattening process is performed so as to enable the thin film to have a thickness profile. Finally, the thin film having a thickness profile is etched, thereby forming a tapered waveguide. However, in this method, it is difficult to control the inclination and the shape of a tapered section. In addition, a separate flattening process is necessary.
According to another conventional method of manufacturing a tapered waveguide, heat is locally applied to the waveguide after a waveguide with a uniform thickness is formed, thereby enlarging a predetermined portion of the waveguide. In this method, a precise control is impossible in forming the waveguide.
In the conventional methods described above, complicated processes are necessary, and there is a limitation in controlling the tapered profile. Further, it is difficult to employ the conventional methods for a mass-production of waveguides.
Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art, by providing a method of manufacturing a tapered optical waveguide, in which an optical waveguide having a construction tapered in vertical and horizontal side views can be manufactured through a simple manufacturing process.
Accordingly, this invention provides a method of manufacturing a tapered optical waveguide, the method comprising the steps of: (1) forming an underclad layer and a core layer in sequence on a substrate; (2) forming a photo-resist pattern having an inclined profile on the core layer by means of a gray-scale mask; (3) etching the photo-resist pattern and the core layer to form a first tapered core layer having a side profile equal to that of the tapered optical waveguide to be manufactured; (4) forming a mask pattern on the first tapered core layer, the mask pattern having a planar profile equal to that of the tapered optical waveguide to be manufactured; (5) etching the first tapered core layer utilizing the mask pattern as an etching mask, thereby forming a second tapered core layer; and, (6) forming an overclad layer on the second tapered core layer.
It is preferred that, in step 2, the inclined profile of the photo-resist pattern can be controlled by adjusting ultraviolet-ray transmittance of the gray-scale mask.
More preferably, in step 3, an inclination of the side profile of the first tapered core layer can be controlled by adjusting an etching-selection ratio between the photo-resist and the core layer.
Another aspect of the present invention provides a method of manufacturing a tapered optical waveguide, the method comprising the steps of: (1) forming an underclad layer on a substrate; (2) forming a photo-resist pattern having an inclined profile on the underclad layer by means of a gray-scale mask; (3) etching the photo-resist pattern and the underclad layer to form a tapered underclad layer having a side profile equal to that of the tapered optical waveguide to be manufactured; (4) depositing a core layer on the tapered underclad layer and flattening the core layer, thereby forming a first tapered core layer; (5) forming a mask pattern on the first tapered core layer, the mask pattern having a planar profile equal to that of the tapered optical waveguide to be manufactured; (6) etching the first tapered core layer utilizing the mask pattern as an etching mask, thereby forming a second tapered core layer; and, (7) forming an overclad layer on the second tapered core layer.